1. Field of the Invention
This invention is in the field of integrated semiconductor circuits including a substrate of silicon, an external contacting track level consisting of aluminum or an aluminum alloy, the contacting track level being connected to the active substrate regions by means of a metal silicide intermediate layer.
2. Description of the Prior Art
External interconnect levels consisting of aluminum or an aluminum alloy have been provided with intermediate layers of platinum silicide to connect the same to the diffused silicon regions, as described in an article by Ting and Wittmer in "Thin Film Solids", vol. 96 (1982), page 331. The reaction temperature is at about 400.degree. C.
The article by Ting and Wittmer also describes metallizations for integrated circuits based on aluminum or aluminum alloys such as aluminum-silicon and silicides. The thermal instability occurs at about 550.degree. C. The metallization system described, however, has some disadvantages. First, the formation of small contacts to flat, highly doped diffusion regions in the silicon substrate is very problematical because of the danger of substrate shorts due to so-called "spiking", and/or epitaxial p-silicon growth into the contacts, resulting in degradation of n.sup.+ contacts.
Second, it is very difficult to manufacture a temperature-stable Schottky diode with a low forward barrier height .phi..sub.B on n-silicon as are required, for example, for "clamped transistors" that are employed in Schottky transistor-transistor logic (TTL) circuits or in combined complementary metal-oxide-semiconductor (CMOS)/Schottky TTL circuits since the aluminum generally diffuses through most low barrier silicides to the interface and increases the barrier height.
These disadvantages can largely be eliminated by providing further layers as diffusion barriers in addition to the contacting silicide layer. For example, a three-layer system consisting of aluminum, titanium and platinum silicide wherein the platinum silicide is located only in the contact hole is described on page 338 of the aforementioned article by Ting and Wittmer.
U.S. Pat. No. 4,201,999 to Howard describes a three-layer system consisting of tantalum, tantalum-aluminum and aluminum for reducing Schottky forward barrier heights on n-silicon. The disadvantage of this type of metallization is that tantalum tends to silicide formation at relatively low temperatures when in contact with silicon, thereby creating the possibility of substrate shorts.
These known layer systems further require additional process steps which add considerably to the cost and which can increase the rejection rates in the manufacture of the integrated circuits.